I own a GT Turbo and they are very similar expect in the rear end. You'll want to look just underneath the seat at the floor pans. Water drips through worn door seals and collects there, If they are bad the car's not a total loss . Frame connectors will shore up the weakened floor pans but you may still have to have them reinforced.
My car has 170,000 miles on it and the turbo has never been rebuilt. but its something you may need to check. If the car has sat a while and not been driven much oil collects and "hardened" in the oil lines cause the turbo to "seize"and can take a while to reheat and work out through short periodic drives.
The car engine is strong with four main bearings but the top ends can wear out if not properly taken care of listen for valve tapping could indicate a broken valve spring or a need for adjustment. The cars are underrated and a good one will give a lot of older V8 cars a run for thier money. Good Luck!